1. Field of the Invention
The present invention relates to an electrolytic cell assembly for the production of bromine for providing brominated water for sanitizing a body of water such as a swimming pool or hot tub. The invention also relates to a process for producing bromine by the electrolysis of sodium bromide in an electrolytic cell.
2. Description of the Related Art
The production of a halogen, especially chlorine, in an electrolytic cell using bipolar electrodes or monopolar electrodes for sanitizing a body of water, especially swimming pools, is known. The Fair et al. U.S. Pat. No. 4,714,534 describe a monopolar electrode system and a bipolar electrode system, the patent being directed to the use of trapezoidal shaped electrode plates used in the monopolar electrode system.
The Sweeney U.S. Pat. No. 4,256,552 discloses a chlorine generator for the chlorination of a body of water. The generator uses bipolar electrodes.
The Davis et al U.S. Pat. No. 4,255,246 discloses an electrolytic cell and method of making hypochlorous acid from aqueous sodium chloride. An electronics control package is shown that is coupled to a source of alternating current and includes typically a rectifier and voltage regulator to provide for a constant but adjustable direct current output voltage across the electrodes of the electrolytic cell.
The Davies U.S. Pat. No. 4,917,782 shows an electrolytic cell including a cylindrical casing for housing a stack of electrode plates and mounting rings to maintain the plates in a fixed position.
The McCallum U.S. Pat. No. 4,142,959 (also related U.S. Pat. No. 4,085,028) is directed to an electrode assembly having bipolar electrode elements for use in producing chlorine. The assembly runs on a.c. current. It is indicated that the problem of unwanted deposits on the bipolar electrodes is reduced by controlling the electrolyte feed solution and by reversing the direction of current flow to the electrodes.
The Shindell U.S. Pat. No. 4,263,114 is directed to treating swimming pool water electrochemically. Shindell uses a.c. current, and rectifies it to apply a unidirectional d.c. current to a pair of electrodes. The method includes reversing the polarity of the energy applied to the electrodes, the feed water flowing past the electrodes. The feed water is, for instance, pool water to which sodium chloride has added to make it electrically conductive.
The Jansen U.S. Pat. No. 4,306,952 is directed to an electrolytic process for producing a halogen, including chlorine and bromine, using an electrolytic cell with bipolar graphite electrode plates. Jansen indicates that reversing the polarity of the plates will help to keep the electrode plates clean. Jansen discloses that the polarity should be changed every 80 to 330 minutes to obtain the benefits of the invention. Jansen uses an electrolytic cell assembly that has one permanent anode and two other anodes, one being a co-anode and the other being a cathode.
The above described patents, especially the McCallum patent and the Jansen patent are incorporated by reference for the description of what is old in the background of the invention.
Also incorporated by reference are pages 671-80, Vol. 8, Third Edition, Kirk-Othmer Encyclopedia of Chemical Technology, 1979, John Wiley and Sons. As therein stated, in discussing electrochemical processing, electrolytic cells, and the electrolysis of brine, cells are often designed with a stack of bipolar electrodes between monopolar feeder electrodes (anode and cathode). The bipolar electrodes are not electrically connected to the d.c. power supply but are polarized by the potential gradients in the cell. Generally, the bipolar anodes are polarized anodically on the side facing the feeder anode electrode and cathodically on the reverse side.
However, the prior patents and the Kirk-Othmer reference do not solve the problems of (1) removing unwanted deposits efficiently from bipolar graphite plates and (2) controlling the flow of electrolyte to provide an efficient flow rate through the cell.